Web drying method and apparatus



Feb. 27, 1968 E. D. BEACHLER WEB DRYING METHOD AND APPARATUS 5SheGES-Sheet l Filed May lO, 1955 ATTORNEYS Feb. 27, 1968 E. D. BEACHLERWEB DRYING METHOD AND APPARATUS 3 Sheets-Sheet 2 Filed May VlO, 1965Feb; 27, 1968 E. D. BEACHLER l 3,370,359

WEB DRYlNG METHOD AND APPARATUS Filed May lO, 1965 'a' Sheets-Sheet 3oem/E55 w e s 0 I@ 2a zo 4a z a 7a a 9o fg 0;- aerfe 5567704/ I N VENTOR. fdl/4rd eaclor A TT() NE YS United States Patent Ofi-ice 3,370,359Patented Feb. 27, 1968 3,370,359 WEB DRYNG RETI-10D AND APPARATUS EdwardD. Beachler, Beloit, Wis., assigner to Beloit Corporation, Beloit, Wis.,a corporation of Wisconsin Filed May 10, 1965, Ser. No. 454,575 19Claims. (Cl. 34-18) The presen-t invention -deals with the drying of webmaterials in such a manner as to accommodate shrinkage withoutsacrificing drying eficinecy. More specifically this invention relatesto the heated vcylinder drying of paper on a papermaking machine whereinthe paper is released from adherence to the cylinders during the periodof maximum shrinkage of the paper.

While the invention will be specifically hereinafter described lasembodied in a process and apparatus for the cylinder drying of paper ona papermaking machine, it should be understood that the principle-s ofthis invention are generally applicable to the drying of web materialswhich shrink during the drying operation. Therefore the scope of thisapplication lincludes the drying of all such materials.

The conventional drying section of 'a papermaking machine includes oneor more heated drums or cylinders receiving the paper therearound inintimate contact therewith. :In the multiple dryer cylinder equippedpapermaking -machines the paper is lapped around successive cylindersand held in intimate contact with the cylinder surfaces by felts. Insingle dryer cylinder equipped papermaking machines, such yas Yankeemachines, a pressure roll is generally provided to squeeze the Wet webon the dryer surface. This intimate contact between the web and theheated drying surface increases the drying efficiency of the cylinderand prevents steam -generated from the moisture in the webfrom liftingthe web out of good :heat transfer relation with the heated cylindersurface.

-In order yto provide intimate contact between the web and the heateddrying surface when felts or press-ure rolls are employed, lthe web isusually tensioned at l pounds per linear inch. Such tensioning of theweb at a particular subsection of the drier is maintained by controllingthe speed of a subsequent subsection. A web tension sensor may beemployed to automatically control a variable speed drive or inchingdrive in the subsequent subsection.

It is known that Wet paper shrinks considerably before it reaches afully dried condition and since intimate contact between the dryingcylinder and the paper web interferes with such shrinkage, `the desiredphysical properties of the dried paper cannot be obtained unless someprovision is made to accommodate shrinkage. Heretofore shrinkageadjustment has only been possible during open draw areas of the web aswhen it passes, unsupported, between dryer cylinders. This adjustment iseffected by varying the relative speeds of the offgoing and oncomingcylinders at `the extremities of the open draw. Thus, it has becomeconventional to divide the dryer section of a papermaking machine into aplurality of subsections each including geared together cylinders. Thedrying capacities of the sections are regulated so that the paper web-will be -delivered to the slower ydriven subsections through open drawsat points in the drying process where the paper is about to pass throughits maximum shrinkage rate. Since the unsupported draws are non-dryingareas, it will be appreciated that compromises must be made in relativespeeds of the successive dryer subsections because the draws must havesome degree of tautness and the web cannot go through its maximumsh-r-inking range unless it continues to lose moisture.

The present invention now provides for the release of the paper fromiadherence tothe drying cylinder While utilizing the cylinder to dry thepaper through its maximum shrinkage range and without interfering withthe efficient drying of the paper in intimate Contact with dryingcylinders outside of the maximum shrinkage range. The present inventionmakes use of the conventional drying -sections of existing paper-makingmachines to dry the paper up to and beyond the maximum or lcriticalshrinkage range and provides drying cylinders for drying the paperthrough its maximum or critical shrinkage range with apparatus forreleasing the paper from adherence to these cylinders so that the papercan shrink while still under the drying influence of the cylinders. Therelease of the paper is Vcaused by high velocity air jets impingedagainst the paper on the cylinders and lifting the paper from adherenceto the cylinder surface so that it is free to assume dimensions inaccordance with its moisture content.

The use of high velocity air jets has heretofore been known and employedfor drying a paper web by impinging such jets against the paper on thecylinders. In such drying operation-s, however, .because of the tensionnormally employed on the paper web, the paper would not be completelylifted from adherence to the cylinder surface. That is, high velocityair jets impinged normally against a paper web on the drying cylinderswould tend to lift the paper from adherence to the cylinder surface,

but the tension normally employed in drawing such a paper web through aplurality of dryer sections would not allow complete release of thepaper from 4the cylinder surface. As a result, the tensions employed onthe paper web in such drying sections were increased to a range ofbetween 20 and 30 pounds per linear inch so as `to achieve completeadherence of the paper web to the cylinder surfaces.

n accordance with the present invention, therefore, high velocity airjets are employed to cause a lifting action on the paper web fromadherence to the cylinder surface while the tension maintained on thepaper web is controlled within a definite range to permit the paper webto lifted.

Since all papers can be partially dried Afrom their as formed conditionwithout appreciable shrinkage and since such papers do not appreciablyshrink after they have passed through a critical moisture range, thecylinv ders equipped with the high velocity air jet arrangementsaccording to this invention need only be `used in those dryer sectionsof the machine Whe-re the paper goes through its critical moisturerange. Generally the critical moisture range for maximum `shrinkage ofthe paper occurs when the paper is from approximately 50% to 85% bonedry.

Therefore, an important feature of this invention is the release ofintimate cont-act of the paper from the drying cylinders of lapapermaking machine in a subsection of the paper machine ldryer sectionas 4by means of high velocity air -jets directed normal to the paper forlifting the paper from the drying cylinders.

Another importan-t feature of the present invention resides in thecontrol of the speed ofthe various subsections of a paper machine dryersection to maintain the proper tension on the paper web passing over thedrying cylin- Iders and impinged with high velocity air jets forallowing the paper to be lifted from the drying cylinders.

In a preferred embodiment of this invention felt equipped dryingcylinders are provided immediately adjacent the offgoing ends of the airjet equipped drying cylinders to lessen the length of the web which isunsupported by felts for .reducing breakage and the tendency of the 'webto be pulled backwards and Wrap around the first cylinder to which itmay adhere.

It is then an object of this invention to release web material fromadherence to heated drying surfaces as it passes through a criticalmoisture content in which maxi- 3 mum shrinkage occurs Without, however,resorting to the use of long open draws of the web material.

A further object of this invention is to take advantage of the ,eicientdrying of web material in intimate contact with heated drying surfacesup to and beyond the moisture range where maximum shrinkage occurs andto release the web material from such intimate contact as it is driedthrough the maximum shrinkage range without, however, resorting to theuse of unsupported draws of the paper.

A further object of the invention is to dry paper in a conventionalmanner on felted drying cylinders only until the moisture content of thepaper is reduced to a point Where the paper starts to `shrinkappreciably and to then continue the drying of the paper on feltlessdrying cylinders equipped with means for lifting the paper out ofadhering contact with such cylinders.

A specific object of this invention is to dry paper on conventional feltequipped drying cylinders down to approximately 50% to 60% bone drynessand to then continue the drying on feltless drying cylinders to a bonedryness of about 85% while lifting the paper out of intimate Contactwith the feltless cylinders by the use of high velocity air jets.

Another specic object of this invention is to interpose feltless dryingcylinders in the drying section of a papermaking machine and to equipsuch cylinders with means for lifting the paper out of adhering contactwith vthe cylinders. t

Another and specie object `of this invention is to prof vide a subdryersection in a conventional multiple cylinder dryer section of apapermaking machine with air hoods which lift the paper olf thecylinders of the subsection to accommodate shrinkage of the paper onlyas it Ypasses through a critical moisture content in which maximumshrinkage occurs and to provide felt equipped drying cylinders at theexiting end of the subsection to reduce the unsupported length of thepaper.

Still another specific object of the present invention is to provide asubdryer section in a conventional multiple cylinder dryer section of apapermaking machine with air hoods which lift the paper oi of thelcylinders of lthe subsection and to control the tension of the paperweb to. within a specified limit such that the paper will be releasedfrom adherence to the cylinder surfaces to allow free shrinkage of the-paper web during a period when the paper web passes through a criticalvmoisture content range.

Other and further objects of this invention will becorne apparent tothose skilled in this art from the following detailed description of theannexed sheets of drawings which, by way of preferred examples only,illustrate several embodiments ofthe invention.

FIGURE 1 is a diagrammatic side elevational view of a dryer sectionaccording to this invention equipped with a feltless subsection at thepoint where the paper web passes through its maximum shrinkage range.

FIGURE 2 is a diagrammatic view illustrating the manner in which thesubsections of the dryer section of FIGURE 1 are driven. i

VFIGURE 3 is a fragmentary side elevational view of an alternatearrangement of a dryer subsection according to this invention. I i

FIGURE 4 is a graph illustrating the shrinkage rate Vof paper at variouspositions in a dryer section such as is shown in FIGURE 1.

FIGURE 5 is a graph illustrating the moisture condition of the paper atvarious portions of the dryer section of FIGURE l1.

FIGURE 6 is a somewhat diagrammatic side elevational view With parts insection of a hood equipped feltless cylinder according to thisinvention. Y Y

FIGURE 7 is a somewhat diagrammatic elevational view of a Yankee dryerincorporating a hood means accordingto this invention.

As shown on the drawings:

In FIGURE 1 the dryer section A includes three subsections 10, 11 and 12with the subsections 10 and 12, being conventional felt equipped gearedtogether multiple drying cylinder sections and the intermediate section11 being a hooded feltless section accommodating free shrinkage of thepaper.

Subsection 10 includes an upper bank or tier of drying cylinders 13a to131' inclusive and a lower bank or tier of drying cylinders 14a to 14hinclusive in staggered relation to the cylinders of the upper tier. Anewly formed paper web W emerging from' the nip of press rolls 15 and 16of the press `section of a conventional papermaking machine is threadedthrough the subsection 1,0 in a serpentine path alternately lapping thetops of the cylinders of the top tier and the bottoms of the cylindersof the bottom tier. An upper tier dryer felt 17 laps a pair of feltdryer or Feeney rolls 18 and 1,9, and a felt return roll 20, and isguided in an open looped path by guide rolls 21 with one of the rolls 21having a felt tensioner attachment. Asimilar bottom dryer felt 22 isprovided and guided by the guide rolls 23 and lapping dryer or Feeneyrolls 24 and 25 and a felt return roll 26. The felts 17 and 18 lap thepaper web W as it passes over the drying cylinders and cause it to bemaintained in intimate contact with the drying cylinder surfaces toobatin maximuur heat transfer from the cylinder to the paper.

The second subsection 11 includes an upper tier ,of drying cylinders 30ato 30d and a lower tier ,of drying cylinders 31a to 31a'. A hood 32envelops the top halves of the top tier of cylinders 30a to 30d while asecond hood'33 envelops the bottom halves of the lower tier of cylinders31a to 31d. As indicated by the arrows the hoods 32 and 33 areadjustable to give access to the cylinders in the event of a web break.The web from the last cylinder 131' of the subsection 10 enters thesubsection 11 under the roll 31a and it will be especially noted that nocovering feltssuch as 17 and 22k are provided for the cylinders 3,0 and31.

FIGURE 6 illustrates a type of hood for the cylinders of the subsection11 and is shown for convenience only in connection with the single dryercylinder 39a. The hood Y 32 could thus be a plurality of individualunits such as is shown in FIGURE 6 or could encompass a plurality of thecylinders as illustrated in FIGURE 1.

As shown in-FIGURE 6 lthe 4hood 32 includes an insulated cover 34coextensive with the width of the rweb W and having a bottom opening 35to encompass the topV half of the cylinder- 30d to be generallycoextensive with the degree of wrapof the web W on theroll 30a. Opposedside walls 36 and 37 and end walls such as 38, a generally flat top wall39, Yand a bottom wall 40 constitute the housing. The housing contains aplurality of blower heads 41a to 41d defining interiorly air supplyplenums fed by conduits 42a to 42d respectively from a supply duct 43connected to a suitable source of heated air. Exhaust openings 45 in thehousing remove moisture bearing air from the hood. Nozzles46a to 46dinclusive, illustra-ted in the form of plates have a plurality of holesor perforations 47 therein of from 1/4 tov 5/3 inch in diameter when theplates are about 1A of an inch thickand when these plates are spacedfrom the web about 1 inch.

Heated air streams issue from the nozzle ,openings 47V at velocities ofthe order of 10,000 to 20,000 feet per minu te to scrub Vfrom the web Wthe boundary layer of mois ture carried by the web and to `release theweb from adherence with the drying cylinder 30a. 'I'his release iscaused -by development of an unbalanced pressure condition on oppositesides of the web produced by a greater air velocity along the exposedweb surface as contrasted with .the pressure on the web surface whichWraps lthe cylinders, In addition, the evaporated moisture between i thedrying cylinder surface and the web creates a vapor pressure tendingtolift the web from the cylinder.

In actual practice, the air which issues from the nozzle openings 47spreads out over the surface of the paper web and .provides a gradientof pressure which decreases from one of the nozzle openings 47 to amidpoint between that and an adjacent nozzle opening. However, as thepaper web is being dried, a tilm of expansible gas is created betweenthe web and the drying surface. This gas, as well as any air that iscarried into the space between the we-b and the drying cylinder bymovement of the web and rotation of the cylinder, cause a pressurediderential across the web which provides a lift thereto. If the tensionon the web is within a prescribed range, the web will be lifted entirelyfrom the cylinder surface allowing free shrink of the paper web. Sincethe web is released from adherence `from the cylinder surface relativefree movement between the web and the surface can occur permitting theweb to shrink to any dimension natural to its moisture content.Throughout the entire shrinking operation, however, the web continues to,be subjected to elicient drying both from the heat of the dryingcylinder surface and the heat of the heated air issuing from the nozzles47. In addition, the moving air sweeps away the moisture ladenatmosphere normally surrounding the -web in a drying section.

included in the second drying subsection 11 and driven at the same rateof speed as the cylinders 30 and 31 is a pair of felt wrapped cylinders50 and 51 equipped with dryer felts 52 and 53 respectively, guided byrolls such as 54. The purpose of these felt equipped cylinders in thesubsection 11 is to minimize an open draw length for the web between thesections 11 and 12 and to prevent the web from wrapping around theIfeltless cylinders in the event of a web break. The felted cylinders 50and 51 are thus eifective to pull the web through the section 11.

The third dryer subsection 12, as shown in FiGURE l, is similar to thesection 16 and includes an upper tier of drying cylinders 66a to dileinclusive, a lower tier of drying cylinders 61a to 61e inclusive, a topfelt 62 wrapping a return roll 63 and guided by roll 64, and a bottomtelt 65 guided by roll 66 and wrapping a return roll 67. The lastcylinders 60e and 61e are normally,sweat dryers which are run cold toeliminate moisture irregularities in the dried web.

Upon leaving the third drier section 12 the web W moves to a calenderstack (not shown) and is further processed in a conventional manner.

As shown in FIGURE 2 the first dryer subsection 10 is driven by anysuitable motive means or prime mover 70 connected by a shaft 71 to agear reducer 72 having an output shaft 73 connected to -the gears whichgear together all of the dryer cylinders in the irst subsection. Thethird dryer subsection 13 has substantially identical drive arrangement,and like numerals with the suffix "a have accordingly been applied tolike parts. The second dryer subsection 11 includes a prime mover or anysuitable motive means 77 connected through a shaft 7S to a gear reducer79 and then through a shaft 80 to the gears of the rolls 30 and 30a aswell as the felted rolls 50 and 51.

As previously mentioned, the tension of the web must be controlledwithin a predetermined range to allow the web to be lifted fromadherence with the cylinder surface. The tension of the web W ispreferably maintained between 5 to 15 pounds per linear inch in thesection 11, and more precisely at pounds per linear inch. This range ofweb tension can be maintained by controlling the speed of the sections10, 11, and 12 with respect to one another. In FIGURE 2, a speed controlS1 is diagrammatically illustrated as being connected to the motivemeans 77 and a speed control 82 as being connected to the motive means70a. In a similar manner, the speed of the section 10 may also bevariably controlled if desired.

Since the web W will exhibit both lateral and longitudinal shrink, thesection 12 will necessarily have to be operated at a slower speed thanthat of the section 10 to CII ` tension on the web W.

If desired the dryer subsection 11 can be divided into a plurality ofsubsections each with felted dryer cylinders supporting the web betweenthe successive feltless cylinder sections. Thus, as shown in FIGURE 3the subsection 111 has two successive subsections 112 and 113. Thesubsection 112 includes the feltless cylinders 114 to 117, the air hoods118 to 126, and the felted cylinders 121 and 122. A dryer felt 123 forthe cylinder 121 is trained around rolls 124 while a dryer felt 125 forthe cylinder 122 is trained around the rolls 126. Identical hoodedcylinders and feited cylinders are provided in the subsection 113 withcorresponding parts bearing the same reference numerals with the suix aadded. The web W-l. enters the subsection 112 around the dryer 116 andenters the subsection 113 around the dryer 1160 and emerges fromsubsection 113 around the felted cylinder 122:1 from which it can passinto the third dryer section such as 12 of FIGURES l and 2. The section113 can have the cylinders thereof geared together and driven at aslower speed than the cylinders of the section 112 to accommodateshrinkage that might occur in the section 112. Alternately, of course,the two subsections 112 and 113 can have the cylinders driven at thesame speed and the interposed felted cylinders can be safety factors toprevent wrap-around of the paper in the event of web breakage. Thetension of the web JV-1 can be controlled by properly maintaining thespeeds of the preceding section and the succeeding section.

As shown by the graph of FIGURE 4 the paper web from the forming andpress section of the papermaking machine has undergone approximately 8%shrinkage prior to entry into the first portion of the first dryersection 10. lf this dryer subsection 10 forms about 45% of the totaldrying capacity of the entire drying section of the machine, the webonly shrinks about 3% as it passes therethrough. From then on shrinkageoccurs at a rapid rate.

It has been discovered that damaging restrained shrinkage of the webdoes not occur until it is approximately 50% to 60% bone dry. Thus, asshown in the graph of FIGURE 5, when the web enters the first dryersubsection 10 at approximately 30% bone dry very little moisture isremoved until the web has traversed approximately 10% of the first dryersubsection whereupon the moisture content is gradually reduced. Assumingthat the iirst dryer subsection 10 comprises about 45% of the totaldryer section A, the web is about 50% bone dry when it leaves the iirstsubsection 10.

it has been discovered that a critical amount of shrinkage occurs in theweb as it is dried from about a 50% lbone dry condition to about an 85%bone dry condition. Thus, as will be seen from the graphs of FIGURES 4:and 5, as an additional 25% to 30% of the dryer section capacity to drythe web up to about bone dry. A

maximum dryness for the web entering the feltless hooded cylindersection is about 60% and a minimum bone dryness for the web emergingfrom this section is about 80% bone dry. Of course, the feltless hoodedcylinder section can have an abundance of drying capacity and the webcan be finished dried in this section or dried up to about a 90% bonedry condition. The last dryer section 12 reduces the moisture content ofthe paper to between 90% to 95% and as shown by the graph of FIGURE 4the shrinkage of the paper is substantially negligible after it hasreached 85% to 90% bone dry conditions.

In general therefore the felted initial dryer subsection or sectionsreduces the moisture content of the paper to a 50% to 60% bone drycondition while the feltless air hooded subsection or sections reducethe moisture content to commercial dryness, or to 80% to 90% bone drywith a final felted section finishing the drying operation. The feltlesscylinder sections of this invention are effective to dry the web throughits critical shrinkage range Where restraint against shrinkage wouldmaterially alter the physical properties of the web.

As illustrated in FIGURE 7, a single drying cylinder equipped Yankeepapermaking machine can have the drying cylinder 130 receiving the webW-2 therearound from a pressure roll 131 which causes the web to hug andadhere to the heated drying surface of the cylinder. According to thisinvention, however, the web VV-Z is released from adherence to thecylinder as it passes through its critical shrinkage range by means ofthe airv impingernent hood 132 which operates in the same manner as thehood 32 of FIGURE 6. The web tension is maintained within a prescribedrange to allow such release of the web W-Z from adherence to theVcylinder surface. Thus, the web W-Z is released from adherence to thecylinder 130 through a critical drying range of from 50% to 60% bone dryto commercial dryness of 90% to 95% bone dry because no subsequent dryersection is provided.

From the above description it will be understood that this inventionprovides for the highly efficient drying of web material which passesthrough a critical shrinkage range as it is dried and which accommodatesfree shrinkage through this range without sacrificing drying efiiciency.Air jets are used to release the web from adherence to its dryingsurface as it passes through this critical shrinkage range.

The'principles of the invention explained in connection with thespecific exemplifications thereon will suggest many other applicationsand modifications of the same. It is accordingly desired that inconstruing the breadth oi the appended claims they shall not be limitedto the specific details shown and described in connection with theexemplifications thereof.

I claim as my invention:

1. The method of drying a wet fibrous web having a moisture contentwhich, if reduced will cause web shrinkage comprising the steps of:

(a) passing the web over a rotating heated cylinder,

(b) impinging a plurality of air streams over the area of the webpassing over the heated cylinder on the opposite side of the web fromthe heated cylinder, to create a film of expansible gas between the weband the surface of the heated cylinder, which in cooperation with theheated air carried to the undersurface of the web causes a liftingaction of the web from the cylinder, and

(c) tensioning the web within a prescribed range to allow the gascreated and the air carried into the space between the web and theheated cylinder to lift the web from the cylinder only aidistancesufficient to eliminate contact of the Web with the Y cylinder.

2. The method of drying wet fibrous material as defined in claim 1wherein the web is tensioned within a range of from 5 to 15 pounds perlinear inch.

3. The method of drying wet material `as characterized in claim 1wherein the web is tensioned to 10 pounds per linear inch.

4. The method of drying wet web material as defined in claim 1 whereinthe air streams impinging on the web have a velocity of between 10,000to 20,000 feet per minute.

5. The method of drying wet web material as defined in claim 4 whereinthe web is tensioned within a range of from 5 to 15 pounds per linearinch.

6. The method of drying wet web material as defined in claim 4 whereinthe web is tensioned to l0 pounds per linear inch. i

'7. The method of removing moisture from web materials comprising thesteps of Y (a) advancing a web intoV wrapping relationship with a first,second, and third series of drying cylinders, (b) applying pressure`against said web whire wrapping the first and third series of dryingcylinders to urge the web into intimate contact therewith7 (c) directingagainst the web while wrapping the second series of drying cylinders aplurality of air. streams, and

(d) tensioning the web while wrapping the second series of dryingcylinders to within a prescribed range to allow the web to be suspendedin close running 8. A method of removing moisture from web material,

comprising the steps of (a) advancing a web into wrapping relation witha first, second and third series of drying cylinders,

(b) applying pressure against said web while wrapping said first andthird series of drying cylinders to urge the web into intimate contacttherewith, Y

(c) directing lagainst the web while wrapping said second series ofdrying cylinders a plurality of high velocity air jets to lift the webfrom said cylinders whereby said web may shrink freely during the dryingthereof,

(d) tensioning the web while wrapping the second series of dryingcylinders to a prescribed range to allow lifting of the web, and

(e) positively advancing the web from the second series of dryingcylinders to minimize the possibility of backward web movement andwrapping of the web `around first series drying cylinders.

9. The method of drying web material which shrinks appreciably as it isdried through a critical moisture content range, which comprises (a)successively lapping the Wet web around a first series of heated dryercylinders,

(b) pressing the cylinder lapped portions of the web into tight contactwith the cylinders,

(c) driving said first series of cylinders at the same speed,

(d) maintaining the drying capacity of said first series 0f cylinderssufiicient to deliver the web with the moisture content just above saidcritical moisture content range,

(e) lapping the thus Vdelivered web around a second series of heateddryer cylinders,

(f) lifting portions of the lapped web from the second series of heatedcylinders to prevent adherence of the web to said second series ofcylinders,

(g) maintaining the drying capacity of said second series of cylinderssufiicient to deliver the Web with a rioisture content below saidcritical moisture range, an

(h) driving said second series of cylinders at a lower rate of speedthan said first series of cylinders to accommodate shrinkage of thewebin saidv second series of cylinders.

10. The method of drying web material which shrinks appreciably as it isdried through a critical moisture content range which comprises Y y (a)successively lapping the wet web around a first series 0f heatedcylinders,

relationship to the second series of drying cylinders.

(b) pressing the cylinder lapped portions of the web into tight adheringcontact with said first series of cylinders,

(c) driving said first series of cylinders at a first speed,

(d) maintaining the drying capacity of said first series of cylinderssufficient to deliver the web 'with a moisture content just above saidcritical moisture content range,

(e) lapping the thus delivered web around a second series of heatedcylinders,

(f) directing heated air jets against the lapped portions of the web onsaid second series of heated cylinders to lift the web and preventadherence of the web to said second series of cylinders,

(g) maintaining the drying capacity of said second series of cylinderssufficient to deliver the web with a moisture content below saidcritical moisture content range,

(h) driving said second series of cylinders at a second rate of speedand slower than the speed of said first series of cylinders toaccommodate shrinkage of the web through said critical moisture contentrange and allow lifting of the web, and

(i) continuing the drying of the web to commercial dryness.

11. The method of drying paper which comprises (a) successively lappinga wet web of newly formed paper around a first series of heated dryercylinders,

(b) covering the cylinder lapping portions of the web with felts,

(c) pressing the felts against the web to maintain intimate contactbetween the cylinders and the web,

(d) driving said first series of cylinders at the same speed,

(e) drying the web with said rst series of cylinders to about 50% bonedry,

(f) lapping the thus dried web around a second series of heated dryercylinders,

(g) impinging heated jets of air against the lapped portions of the webon said second series of heated cylinders to lift the web from aheringcontact with said second series of heated cylinders and to continuouslymaintain said web freely suspended over such heated cylinders bycontinued application of such heated air jets to afford unrestrainedshrinkage of the web in all directions at least until it is dried tosubstantially 35% bone dry, and

(h) driving said second series of heated dryer cylinders at a speedsufficient to maintain the tension of the web passing thereover towithin a range of from to l5 pounds per linear inch.

12. The method of drying a paper web on a paperrnaking malicine whichcomprises (a) successively lapping the wet web around a first series offelt-covered heated dry cylinders,

(b) driving said first series of cylinders at a first rate of speed,

(c) maintaining the drying capacity of said first series of cylinderssufficient to deliver the web with a moisture content just above thecritical moisture content range for the paper Where the maximumshrinkage of paper occurs,

(d) lapping the thus delivered web around a second series of heateddryer cylinders including an initial group of feltless cylinders and afinal group of felt covered cylinders,

(e) irnpinging heated air jets against the web on the feltless cylindersto lift the web from said feltless cylinders,

(f) maintaining the drying capacity of said second series of cylinderssufficient to dry the web through its critical moisture range, and

(g) driving said second series of cylinders at a speed j sufficientlyslower than said first series of cylinders to accommodate shrinkage ofthe web as it passes over the feltless cylinders of said second seriesof cylinders and sufficiently to allow lifting of the web. 13. Apparatusfor drying web material which shrinks appreciably as it is dried througha critical moisture con- 5 tent range which comprises (a) `a firstseries of geared together dryer cylinders for successively receiving thewet web in lapped relation therearound,

(b) covering felts for said rst series of cylinders to hold the web inintimate contact with the cylinders,

(c) means 4driving said first series of cylinders at a first speed,

(d) a second series of geared together dryer cylinders for receiving theweb from said first series of cylinders, said second series of cylindersincluding a first group of feltless cylinders and a second group of feltcovered cylinders receiving the web from said first group,

(e) air impingernent means for said first group of feltless cylinders insaid second series of cylinders effective to prevent adherence of theweb to the feltless cylinders, and

(f) means driving said second series of cylinders at a slower rate ofspeed than said first series of cylinders for accommodating shrinkage ofthe web and for tensioning the web to within a range to allownonadherence of the web to the feltless cylinders.

14. Apparatus for removing moisture from web material which comprises:

(a) a rst dryer section including a plurality of drying cylinders gearedtogether for equal peripheral surface speeds and arranged for receivinga web in wrapping relation thereon,

(b) means urging the web into intimate Contact with the cylinders ofsaid first dryer section toreduce the moisture content of the web to apredetermined level,

(c) a second dryer section including a second plurality of dryingcylinders geared together independently from said first plurality forequal peripheral surface speeds adjustable with respect to theperipheral speeds of said cylinders of the first dryer section andeffective to dry the web from the first section to a moisture levelbelow which appreciable shrinkage of the web will not occur,

(d) means urging the web into intimate contact with at least the finalcylinder of said second dryer section to prevent major movement of theweb relative to the surface of said final cylinder,

(e) air impingement means in close proximity to the remaining cylindersin said second dryer section for directing high velocity'air jets tolift the web out of adhering contact with said cylinders whereby the webis free to shrink as it is dried in said second dryer section, land (f)means for controlling the tension of the web in said second dryersection.

15. Apparatus for drying paper webs and the like which comprises (a)first, second and third dryer sections, said first and third dryersections each including a series of geared together felt covered dryercylinders, said second dryer section including a series of uncovereddryer cylinders,

(b) means associated with said uncovered dryer cylinders to preventadherence of the web to said cylinders, and

(c) means driving the cylinders of said second section at a differentrate of speed than the cylinders of said first section to accommodatefree shrinkage of the web and non-adherence of the web to said cylinder.

16. Apparatus for removing moisture from web materials, comprising (a) afirst dryer section including a plurality of drying cylinders receivinga web in wrapping relation thereon,

(b) means urging the web into intimate contact with the cylinders in thefirst section to reduce the moisture content of the web to apredetermined level,

(c) a second dryer section including a plurality of drying cylindersreceiving the web from the first section and at said predeterminedmoisture level, and

(d) air impingement means positioned in close proximity to the cylindersin the second section and directing against the web while in said secondsection air jets of a velocity suilicient to generate lift in the web,whereby during the drying of the web said 'web is released from saidcylinders and may undergo maximum shrinkage.

17. Apparatus for removing moisture from web materials, comprising (a) airst dryer section including a plurality of drying cylinders receiving aweb in wrapping relation thereon,

(b) means urging the web into intimate contact with the cylinders in therst section to reduce the moisture content of the web to a predeterminedlevel,

(c) means driving the cylinders in the rst dryer section at a iirstspeed,

(d) a second dryer section including a plurality of drying cylindersreceiving the web from the first section and at said predeterminedmoisture level,

(e) air impingement means positioned in close proximity to the cylindersin the second section and directing against the web While in said secondsection air jets of a velocity sufficient to generate lift in the web,whereby during the drying of the web said web is released from saidcylinders and may undergo maximum shrinkage,

(f) means driving the cylinders in the second ldryer section at a secondspeed,

(g) a third dryer section including a plurality of drying cylindersreceiving the web from the second section,

(h) means urging the web into intimate contact with the cylinders in thethird dryer section to remove further moisture from the web,

(i) means driving the cylinders in the third dryer section at a thirdspeed, and

(j) means for independently adjusting said first, second and thirdspeeds through a limited range.

Cil

18. Apparatus of the character defined in claim 16 in which there isprovided means to hold the web against backward movement.

19. Apparatus for drying web material, comprising (a) first travellingheating surface means contacting the wet web and removing moisturetherefrom-until its moisture content is at a point at which furtherdrying will cause appreciable web shrinkage,

(b) felt means maintaining the web in engagement with said heatingsurface means,

(c) second travelling heating surface means receiving said web from saidfirst travelling heating surface means, and

(d) means releasing said web from adhering contact with said secondheating surface means during the drying thereof, whereby said web mayfreely shrink and assume dimensions natural to its moisture contentcomprising:

(e) means ejecting heated air on the surface of the web opposite fromsaid heating surface means and creating a lm of expansible gas betweensaid heating means and the web and cooperating with the air carried intothe space between the web and the heating surface means, to lift the webfrom said heating surface means, and

(f) means maintaining suicient tension on the web to limit lifting ofthe web to only the extent necessary to eliminate contact of the webwith the cylinder.

References Cited UNITED STATES PATENTS 1,573,297 2/1926 Briner et'al.34-18 X 2,130,665 9/1938 Bradner 34-23 2,219,857 10/1940 Weston 34-1212,281,496 4/1942 Hanson 34-18 X 2,919,495 1/1960 Underhay et al. 34-160X 3,057,079 10/1962 Schmidt 34--156 3,085,347 4/1963 Justus 34,-160 X3,089,252 5/1963 Daane et al. 34--114 3,257,734 6/1966 Boadway et al'.34-156 X 3,279,091 10/ 1966 Freuler 34-156 KENNETH W. SPRAGUE, PrimaryExaminer.

1. THE METHOD OF DRYING A WET FIBROUS WEB HAVING A MOISTURE CONTENTWHICH, IF REDUCED WILL CAUSED WEB SHRINKAGE COMPRISING THE STEPS OF: (A)PASSING THE WEB OVER A ROTATING HEATED CYLINDER, (B) IMPINGING APLURALITY OF AIR STREAMS OVER THE AREA, OF THE WEB PASSING OVER THEHEATED CYLINDER ON THE OPPOSITE SIDE OF THE WEB FROM THE HEATEDCYLINDER, TO CREATE A FILM OF EXPANSIBLE GAS BETWEEN THE WEB AND THESURFACE OF THE HEATED CYLINDER, WHICH IN COOPERATION WITH THE HEATED AIRCARRIED TO THE UNDERSURFACE OF THE WEB CAUSES A LIFTING ACTION OF THEWEB FROM THE CYLINDER,AND